1. Field of the Invention
The present invention relates to a right/left driving torque distributing device for a vehicle, such as an automobile, and, more specifically, to a right/left driving torque distributing device for a vehicle, capable of varying driving torque distribution ratio in which driving torque is distributed to a right driving wheel and a left driving wheel of the vehicle.
2. Description of the Related Art
Various right/left driving torque distributing devices for vehicles have been developed and put to practical uses in recent years to secure traction and to improve traveling stability when vehicles travel rugged roads. A recently proposed right/left driving torque distributing device is capable of positively controlling driving torque distribution ratio in which driving torque is distributed to right and left wheels to improve the turning performance of a vehicle.
A prior art right/left driving torque distributing device disclosed in JP-A No. 5-77653 comprises a differential gear unit employing a double-pinion planetary gear mechanism having a differential gear case, a ring gear formed on the inner circumference of the differential gear case, a second output shaft, a sun gear mounted on the second output shaft, a first output shaft and a planet carrier mounted on the first output shaft, and a driving torque transmission control mechanism for controlling driving torque distribution ratio in which driving torque is distributed to right and left wheels, combined with the differential gear unit.
The driving torque transmission control mechanism comprises speed change mechanisms associated respectively with the first and the second output shaft to vary the respective rotating speeds of the first and the second output shaft, auxiliary driving torque transmitting members which operate at rotating speeds controlled by the speed changing mechanisms and different from those of the first and the second output shaft, respectively, and a hydraulic multiple-disk clutch for regulating driving torque distribution to the right and the left wheel.
The differential gear unit, and the friction disk units of the multiple-disk clutch mechanism are contained in a differential gear case. The piston unit of the multiple-disk clutch mechanism is disposed outside the differential gear case.
Since the prior art right/left driving torque distributing device disclosed in JP-A No. 5-77653 comprises the differential gear case with the ring gear formed on the inner circumference thereof, the friction disk units provided with drive friction disks and driven friction disks in an alternate arrangement and disposed in a left and a right portion of the differential gear case, respectively, the double-pinion planetary gear mechanism disposed in a central portion of the hydraulic multiple-disk clutch, the auxiliary driving torque transmitting members disposed outside the differential gear case and driven for rotation at rotating speeds controlled by the speed changing mechanism and different from those of the first and the second output shaft respectively for driving the right and the left wheel, and a speed changing mechanism for changing the respective rotating speed of the right and the left output shafts, and those components are arranged in a straight arrangement, the right/left driving torque distributing device has a relatively large lateral size.
Accordingly, the length of each of the drive shafts extended between the output shafts, and the right and the left wheel for rotatively driving the right and the left wheel for rotation is inevitably relatively short and the angle of bend of constant-velocity joints attached to the opposite ends of each drive shaft is inevitably large. Consequently, strength and transmission efficiency of the constant-velocity joints are reduced, and there is the possibility that the constant-velocity joints vibrate and generate noise.
Since the auxiliary driving torque transmitting members for distributing driving torque to the right and the left wheel are disposed on the opposite sides of the differential gear case, the right/left driving torque distributing device is relatively large, has a relatively complicated construction, needs an increased number of component parts, has an increased mass and requires high manufacturing cost.
Since there is a limit to the maximum outside diameter of the friction disks of the hydraulic multiple-disk clutch, the number of the friction disks must be increased greatly or the pressure receiving area of the piston must be increased to increase the torque transmission capacity of the hydraulic multiple-disk clutch. Therefore, the right/left driving torque distributing device designed for use in combination with a high-power automotive engine requiring a large torque transmission capacity is inevitably large, has a large mass and requires a high cost.
Since the left planetary gear and the left piston, the differential gear and the hydraulic multiple-disk clutch contained in the differential gear case, and the right planetary gear and the right piston are assembled in three separate blocks, it is difficult to lubricate those components properly.
A right/left driving torque distributing device employing a double-pinion planetary gear mechanism, disclosed in JP-A No. 5-345535 has a driving torque transmission control mechanism for controlling driving torque distribution ratio in which a driving torque is distributed to the right and the left wheel of a vehicle, interposed between a pair of drive shafts for rotatively driving the right and the left wheel. The driving torque transmission control mechanism comprises a speed augmenting/reducing mechanism having, in combination, a speed augmenting mechanism which increases the rotating speed of one of the pair of drive shafts to an increased rotating speed and drives a first intermediate shaft for rotation at the increased rotating speed, and a speed reducing mechanism which reduces the rotating speed of the same one of the pair of drive shafts to a reduced rotating speed and drives a second intermediate shaft at the reduced rotating speed, a first variable-capacity torque transmitting means, and a second variable-capacity torque transmitting means. The first and the second variable-capacity torque transmitting means are disposed contiguously and united together. Each of the first and the second variable-capacity torque transmitting means comprises an electronically controlled hydraulic multiple-disk clutch.
In the right/left driving torque distributing device, the driving torque transmission control mechanism, the three-pinion speed augmenting/reducing mechanism, and the two hydraulic multiple-disk clutches are arranged in a laterally straight arrangement. Therefore, the right/left driving torque distributing device has a relatively large lateral size and has the same problems as those of the foregoing prior art right/left driving torque distributing device.
Input driving torque applied to the differential gear is distributed properly to the right and the left output shaft of the differential gear by the agency of the speed augmenting/reducing mechanism and the hydraulic multiple-disk clutches. The driving torque distribution ratio in which the input driving torque is distributed to the right and the left output shaft of the differential gear can be controlled by properly varying torques transmitted by the multiple-disk clutches.
Since the double-pinion differential gear mechanism has a large ring gear, large pinions, small pinions and the sun gear, the ring gear must be supported in bearings disposed asymmetrically with respect to the ring gear because there are restrictions on a housing space in the ring gear. Therefore, the bearings are loaded differently, which is disadvantageous in respect of durability, reliability and gear noise.
The differential gear case of this prior art right/left driving torque distributing device needs at least five highly rigid walls. Therefore, the right/left driving torque distributing device has a complicated construction, needs a high manufacturing cost, has a large mass, and is disadvantageous in the balance of lubrication, loss resulting from the stirring action of the multiple-disk clutches and such. Moreover, since the case of the right/left driving torque distributing device is divided into complex divisions, the case has many joining surfaces to be provided with oil seals to prevent the leakage of the lubricating oil, which is disadvantageous in reliability and manufacturing cost, and is able to employ only a few currently produced parts.
A right/left driving torque distributing device disclosed in JP-A No. 1-182127 comprises an input shaft, a differential gear case driven for rotation by the input shaft, pinion shafts fixed to the inner surface of the differential gear case opposite to each other, a pair of differential pinions (bevel gears) mounted on the pinion shafts, respectively, and a pair of side gears engaged with the differential pinions.
Hydraulic multiple-disk clutches are mounted on an intermediate shaft at positions on the side of a right wheel and on the side of a left wheel, respectively, a left output shaft and a right output shaft are coupled with the intermediate shaft by the hydraulic multiple-disk clutches, respectively. Driving torque distribution ratio in which driving torque is distributed to the right and the left wheel is varied according to the traveling condition of the vehicle.
Since this prior art right/left driving torque distributing device distributes driving torque to the right and the left wheel through the hydraulic multiple-disk clutches disposed separately on the intermediate shaft on the side of the right wheel and on the side of the left wheel, respectively, the prior art right/left driving torque distributing device has an increased lateral size and needs an increased number of parts.